Other multi-layer print processes exist and some have been patented such as the process under U.S. Pat. Nos. 5,414,947; 5,682,697; European Patent No 0607261 B.
In that process, the Foreground Graphic Elements are physically separated from their surrounding Background Graphic Elements. The Background Graphic Elements are applied on the back of the clear substrate along with some extra layers of ink or films behind these. A white Reflection copy in the shape of the Foreground Graphic Elements is applied onto the front surface of the substrate in register with the back so that its shape covers the hollow areas of the Background Graphic Elements. The Foreground Graphic Elements are applied onto the front of the said white Reflection layer in register with the back. The light from the light-source then passes through the openings of the back layers (i.e. the shapes left open by the absence of the text or logos that now reside on the front of the substrate). When the light passes through these openings and through the clear substrate, it hits a white Reflection layer on the front of the substrate (which is in the shape of the text or logos) and is reflected back onto the surrounding Background Graphic Layer. The opening on the back is made larger then the graphic element on the front, i.e. its hollow shape is bolder. A fundamental aspect of this invention is that the Background Graphic Elements are applied onto the back surface of the clear substrate and the Foreground Graphic Elements are applied onto the front surface of the said substrate.
The above method produces visual lighting effects that change the viewer's perception of the graphic design, giving perceived relief effect to the Foreground Graphic Elements (e.g. the text or logos) and can also give an aura around the said graphic elements.
But the method has certain limitations, as some colour-combinations are not possible without drastically changing their perception. For example, when attempting to achieve coloured aura around a white Foreground Graphic Element (such as text or logo), the Foreground Graphic Element will appear colour-polluted once backlit—the light transmitted through it will already have transmitted through the underlying colour and thus be coloured light.
The most common manufacturing process for producing displays using the above and similar methods (i.e. the application of colour layers onto substrate) is screen-printing and adhesive film (sign-foil) application. The method mentioned above requires high level of opacity in the inks used in printing in order to produce the required effects. However, in the screen-printing industry, recent developments in ink manufacture have resulted to a shift from solvent-based inks to a new type—UV inks. These inks are more environmentally friendly but are more transparent than solvent-based.